Catalysts comprising a catalytically active metal on a support such as silica or alumina are known in the art for hydrogenation reactions. For example, a catalyst comprising platinum and rhenium supported on alumina has been found to be highly effective for the reforming of naphtha. Similarly, a catalyst comprising cobalt and rhenium supported on alumina or silica has been found to be effective for the preparation of hydrocarbons from synthesis gas via the Fischer-Tropsch process. Although rhenium is an expensive metal, its excellent catalyst promoting activity justifies its commercial use.
In certain chemical reactions, it is believed to be advantageous to deposit a catalytic metal or metals on a titania support. For example, cobalt and rhenium supported on titania is preferred by some workers for Fischer-Tropsch reactions because it is more active for CO conversion than when supported on alumina or silica. Also, titania supported catalysts may be preferred for use in hydrothermal environments where alumina supports may show a tendency to degrade to some extent.
As is well known, during use catalysts tend to become less active and require periodic regeneration. Regeneration typically restores the activity of the catalyst to a level approximating its original condition; however, after many regenerations, the catalyst will no longer be capable of being restored to a satisfactory activity level. It then becomes necessary to replace the deactivated or spent catalyst with fresh catalyst.
Noble catalytic metals are expensive, and hence, the art is replete with methods for recovering them from deactivated catalysts containing them. For example, platinum can be recovered from alumina supported platinum-containing catalysts by dissolving the support with strong acidic or strong basic solutions. Similarly, rhenium can be recovered from alumina supported rhenium-containing catalyst by digestion of the support with an acid or base followed by filtration to isolate the rhenium-containing catalytic metal. This approach is not feasible with titania-supported catalysts because titania is not completely soluble in acid or base.
An object of the present invention is to provide a method for the recovery of rhenium from titania-supported catalysts and especially the recovery of cobalt and rhenium from titania-supported cobalt and rhenium catalysts.